Energy storage systems for many different machines are well known and widely used. Systems such as regenerative braking systems known from mobile vehicle applications may store energy from decelerating a vehicle that would otherwise be lost in an electrical energy storage device such as a battery or a capacitor. Hydraulic systems commonly store energy for subsequent recovery in pressure accumulators or the like. Flywheels have been used for literally centuries to store kinetic energy, and are now increasingly applied in mobile vehicle and machinery applications. A flywheel stores kinetic energy in a rotating rotor that can be sped up to store energy when extra energy is available, and slowed down to extract the stored energy when desired. High-speed flywheels, having rotational speeds in the tens of thousands of revolutions per minute, are commercially available and have been applied now with some commercial success in the automotive context.
One technical challenge relating to high-speed flywheels is the relatively great speed difference between a charged or energized flywheel and the system with which it interacts. In the case of an internal combustion engine, the engine speed may be as much as a few thousand revolutions per minute, but still potentially an order of magnitude or more less than potential speeds of the flywheel. As it is generally desirable to use a relatively small and lightweight flywheel that will rotate relatively fast, as opposed to a heavy, bulky, and slower flywheel, apparatus is typically necessary for matching the speeds of the two systems.
Since many mechanical transmission systems can have inherent structural and material limitations as to the maximum speeds and/or speed ratios within the system, multi-range transmission systems have been proposed to account for the large speed ratios in flywheel energy storage systems. Engineers have also proposed continuously variable transmission or “CVT” systems to transfer torque between a flywheel and an engine or other mechanism having a prime mover. U.S. Pat. No. 9,108,625 proposes a planetary gear device between a driving wheel and an energy accumulating device. A sun gear of the planetary gear device is connected to an input shaft of the energy accumulating device. A carrier of the planetary gear device is connected to the driving wheel. A torque adjusting device is apparently electronically controlled to vary a braking torque applied to a ring gear in the planetary to reduce a difference in rotational speeds between an input shaft and the sun gear. While the strategy in the '625 patent may have certain applications it is relatively complex, and there is ample room for improvements and other advancements in the field.